1. Field of the Invention
The present invention relates to an image recording apparatus that comprises a plurality of printing units and a plurality of drums, and makes image recording.
2. Description of the Related Art
For example, an inkjet printer that makes high-speed image recording of high quality on a recording medium, which is held and conveyed by a conveyance mechanism, by emitting ink droplets from a plurality of nozzles is cited as an image recording apparatus.
This inkjet printer is widely used as a printer for office use, which records an image, for example, on a cut-sheet recoding medium (paper). Additionally, the throughput of an inkjet printer has been improved in recent years by configuring a line head where many printing heads are aligned and arranged in a direction orthogonal to the conveyance direction of a recording medium. An inkjet printer is also used as a printer for industrial use, which records an image on a recording medium (continuous paper) such as roll paper, etc.
A rotational drum that holds and conveys continuous paper such as roll paper, etc. by winding the paper around its perimeter face can be cited as one of effective means for holding and conveying continuous paper in such an image recording apparatus.
Patent Document (Japanese Published Unexamined Patent Application No. 2003-63707) discloses the invention related to the configuration of an image recording apparatus that conveys continuous paper with the above described drum, and can make double-sided printing. The conveyance mechanism of the above described patent document is configured with first and second drums for holding a recording medium by winding the medium around their perimeter faces, a paper conveying unit that is arranged on the upstream side of the conveyance path of the recording medium and on the upstream side of the first drum, and a paper puller unit that is arranged on the downstream side of the conveyance path of the recording medium and on the downstream side of the second drum.
The paper conveying unit and the paper puller unit are composed of conveying rollers made of stainless steel, and driven rollers made of rubber, which are pressed against the conveying roller via a recording medium. A motor is connected to each of the conveying rollers. The conveyance speed of the paper puller unit, which is arranged on the downstream side of the conveyance path, is positively set to become faster than the conveyance speed of the paper conveying unit, which is arranged on the upstream side of the conveyance path. Additionally, the conveying force of the paper puller unit is set to a value smaller than that of the paper conveying unit, so that the conveying rollers of the paper puller unit and the recording medium always slide. With this configuration, the recording medium does not become loose on the first and the second drums, and can be conveyed in close contact with the perimeter face.
Additionally, a first position detecting unit for outputting an accurate electric pulse in accordance with the rotational amount of the first drum is attached to the first drum. A first printing unit arranged at the perimeter of the first drum emits an ink to the recording medium in synchronization with the electric pulse output from the first position detecting unit. Similarly, a second position detecting unit for outputting an accurate electric pulse in accordance with the rotational amount of the second drum is attached to the second drum. A second printing unit arranged at the perimeter of the second drum emits an ink to the back side of the recording medium, which is recorded by the first printing unit, in synchronization with the electric pulse output from the second position detecting unit. As described above, the image recording apparatus conveys the recording medium with the paper conveying unit and the paper puller unit, and can make double-sided printing.